Six NIH-supported investigators from the University of New Mexico seek a new high-resolution scanning electron microscope with the ability to detect backscattered electrons. This instrument will replace an eleven-year old scanning electron microscope which has generated data for well over 100 publications since its purchase in 1974. The manufacturer of the eixsting instrument is no longer in business, and it is anticipated that service and maintenance will become increasingly uncertain. The existing instrument is the only scanning electron microscope in the Albuquerque area available for biomedical research. Purchase of a new scanning electron microscope will guarantee that the research projects at the University of New Mexico requiring scanning electron microscopy will continue uninterrupted for the foreseeable future. In addition to assuring the uninterrupted continuation of research using the scanning electron microscope, the new microscope proposed in this application will enhance the present SEM capability at the University of New Mexico because of its increased resolving power (2 nm guaranteed vs. 10 nm guaranteed on the present instrument), and its ability to simultaneously detect and display secondary and backscattered electrons (for immunocytochemical applications).